Polyurethanes, resulting from the polyaddition of polyisocyanates and polyhydroxyl compounds, are broadly used in the form of reactive one or two component systems as adhesives, sealing materials, decorative or protective coatings and floorings. In all these applications their resistance against ageing and attack by chemical substances, such as for example water, are of great importance. For this reason, a high hydrophobicity of the binder is desired in order to reduce the effects of polar chemicals on the coating or the adhesive. In addition to the chemical resistance, in particular for coatings, aesthetic aspects are of great importance. Therefore, defect-free surfaces are important and for floorings intended for application outside of buildings a resistance against yellowing due to exposition to UV-radiation is required.
Besides of these requirements directed to the features of the cured products, high reactivity or short curing times at room temperature are important, since thereby the processing times can be shortened and the costs of the bound money can be reduced. Furthermore, for the applications in building construction, a sufficiently high reactivity of the systems is a necessity for applications at temperatures around 10° C. This is of great importance since in a lot of geographic regions the average of the application temperatures during a great part of the year is in this range.
It is known for a long time that because of its high hydrophobicity castor oil is a very suitable polyol for two component polyurethane systems. Thereby castor oil is often used mixed with other polyols. By epoxydation and thereon following cleavage of the ring with glycols, castor oil and other plant oils can be reacted to as well hydrophobic polyols, that are suitable for the application in two component polyurethane systems. The patent documents WO 96/06123, U.S. Pat. No. 5,512,655 and DE 4308097 describe such polyols. EP 0 798 325 describes a further polyol that is obtained by reaction of castor oil with aromatic polyesters.
Castor oil and the derivatives thereof (such as ricinoleic acid, methylricinoleate, 12-hydroxy stearic acid methyl ester), as well as the above described reaction products, however, all are characterised by relatively low reactivity with regard to isocyanates, due to the steric hindrance of the therein comprised hydroxyl groups. The above mentioned polyols therefore are unsuitable for reaction with aliphatic isocyanates at room temperature, in order to obtain UV-stable non yellowing systems. The reaction with the much more reactive aromatic isocyanates, such as MDI and its derivatives, is possible, the reaction products of the above described polyols with aromatic isocyanates, however, have a great tendency for yellowing at the exposition to light. Furthermore, due to the low reactivity of the secondary hydroxyl groups very fast systems for spraying applications can only be realised in a very restricted scope. Furthermore, the secondary hydroxyl groups very often do not entirely react with the isocynates groups. The remaining not reacted hydroxyl groups often lead to a much enhanced hydrophilicity of the systems and reduce their life-time.
Polyester polyols with enhanced reactivity are described in the patents U.S. Pat. No. 4,656,243, U.S. Pat. No. 4,692,384, U.S. Pat. No. 4,894,430, U.S. Pat. No. 5,260,138 and U.S. Pat. No. 5,319,056. These polyols show a sufficient reactivity to enable a reaction with non-aromatic isocyanates at room temperature In comparison with the above described polyols, however, they have a much reduced hydrophobicity.